It has an electric motor and a conventional engine, and it can't be classified as a zero-emissions vehicle but whatever you do, don't call the GM Volt a hybrid!

"It's an electric vehicle," states Johan Willens, GM's global director of advanced propulsion and environmental communications. "The electric motor drives the wheels at all times." It has a 16KwH Lithium Ion battery pack that gives the Volt a range of around 40 miles sufficient for most everyday use.

But what's different is the Volt's small petrol engine, which isn't coupled to the drivetrain but acts as a generator, recharging the battery when it's out of juice. So Volt owners won't be stranded if they travel for more than 40 miles.

"We call it a range extender," says Willens. In fact, GM calls the concept E-REV extended-range electric vehicle and it'll play a major role in GM's environmental plans in the future.

The Volt was shown at Paris in production-ready form and it has changed a lot since the original Volt concept was unveiled at the 2007 Detroit Show. It's a much more rounded shape now, and Willens says the changes are necessary in order to optimise the Volt's aerodynamic efficiency which helps add precious miles to the range.

Volt will go on sale in the US at the end of 2010, but Europe is likely to receive other models using the E-REV concept possibly a version of the next-generation Zafira, which will use the same platform as the Volt, but whose MPV body is more likely to appeal to European tastes than the Volt's four-door saloon.

"The system can drop in to other cars in the GM range," says Willens. What's more, the petrol 'generator' could be replaced by fuel cells in the future, when the technology becomes available at the right price.

What has enabled GM to produce an E-REV is the advance in battery with Lithium Ion technology. Indeed, Willens says the concept is not a new one: "We were working on a similar four-door car under the EV-1 project in the 1990s, but it wasn't possible because of the battery technology.

He says most users won't travel for more than 40 miles a day which could mean the generator is rarely used. This has created other issues, such as oil pooling in the generator, though Willens says GM has come up with solutions for this.